LESSON 18.] 



OVULES. 



123 



instance of it : it is shown in its place in the ovary in Fig. 268, 

 also detached in Fig. 270, and a much more magnified diagram of it 

 in Fig. 274. In this kind, the orifice (/) is at the top, the chalaza 

 and the hilum (c) are blended at the base or point of attachment, 

 which is at the opposite end ; and the axis of the ovule is straight. 

 /._.. 



If such an ovule were to grow on one side more than on the other, 

 and double up, or have its top pushed round as it enlarges, it would 

 become a 



Campylotropous or curved ovule, as in Cress and Chickweed (Fig. 

 271). Here the base remains as in the straight kind, but its apex 

 with the orifice is brought round close to it. Much the most com- 

 mon form of all is the 



Anatropous or inverted ovule. This is shown in Fig. 267, and 

 273 ; also a much enlarged section lengthwise, or diagram, in Fig. 

 275. To understand it, we have only to suppose the first sort (Fig. 

 270) to be inverted on its stalk, or rather to have its stalk bent 

 round, applied to one side of the ovule lengthwise, and to grow fast 

 to the coat down to near the orifice (jf) ; the hilum, therefore, where 

 the seed-stalk is to break away (h), is close to the orifice ; but the 

 chalaza (c) is here at the top of the ovule ; between it and the hilum 

 runs a ridge or cord, called the Rhaphe (r), which is simply that part 

 of the stalk which, as the ovule grew and turned over, adhered to its 

 surface. Lastly, the 



Amphitropous or half-anatropous ovule (Fig. 272) differs from 

 the last only in having a shorter rhaphe, ending about half-way 

 between the chalaza and the orifice. So the hilum or attachment is 

 not far from the middle of one side, while the chalaza is at one end 

 and the orifice at the other. 



326. The internal structure of the ovule is sufficiently displayed 



the subjoined diagrams, representing a longitudinal slice of two 



FIG. 270. Orthotropous ovule of Buckwheat: c, hilum and chalaza; /, orifice. 



FIG. 271. Campylotropous ovule of a Chickweed : c, hilum and chalaza ; /, orifice. 



FIG. 272. Amphitropous ovule of Mallow : /, orifice ; A, hilum ; r, rhaphe ; c, chalaza. 



FIG. 273. Anatropous ovule of a Violet ; the parts lettered as in the last. 



